Page:Popular Science Monthly Volume 75.djvu/34
THE POPULAR SCIENCE MONTHLY.
where the arrows FF in the top view represent the forces with which the bearings must act upon the engine shaft to produce the torque T.
Gyrostatic Action of a Rolling Disk
Fig. 23 represents a penny rolling along a floor. The forces FF in the side view (the tendency of the penny to fall over) constitute a torque which is represented by the arrow T in the top view. This torque produces during a short interval of time an increment of spin-momentum
ΔS which, added to the existing spin-momentum S, gives the resultant spin-momentum S' in the direction of which the axis of the penny is found to be turned. The result is that the penny rolls along a circular path as represented by the dotted curve in the top view,Fig. 23. The wheels of a bicycle exhibit a gyrostatic reaction when